Path loss is a measure of signal attenuation. Path loss is the difference between the transmitted signal power and the received signal power. Path loss has the units of Decibels (dB) and is a positive quantity which excludes the affects of the antenna gains. In its simplest form, path loss can be defined according to the free-space model of equation (1):PL(dB)=Pt−Pr  (1)where PL denoted path loss, Pt is the signal's transmitted power level and Pr is the signal level recorded at the receiver, measured in units of decibels, such as dBm. Equation (1) assumes that there is no antenna gain at the transmitter and the receiver.
Path loss is least pronounced where a visible line of sight is available between the transmitter and the receiver where there is little or no electromagnetic interference. Electromagnetic interference is typically in the form of co-channel interference. Conversely, path loss is more pronounced as obstacles and electromagnetic sources interfere with signal propagation. Because path loss is a measure of signal attenuation, and therefore, bit error rate, it is an important tool in measuring quality of service throughout a wireless network.
In wireless networks, service quality across geographic areas is audited by conducting drive tests. In such tests, a transmitter is positioned at different locations to send a beacon signal. The transmitter's signal level and the location of the transmitter are recorded. The receivers then record the received signal level. Using the transmitted and received signal levels, path loss between the two locations can be computed.
Once a frequency channel is dedicated to the path loss measurement, the transmitter's signal strength for the beacon signal and its location are recorded. The receiver then measures and records the received signal strength. Using the transmitted and received signal strengths a processor can determine the path loss value at the transmitter's location.
Dedicating a specific channel for path loss measurements and rearranging the remaining channels on the frequency use plan to accommodate the path loss-dedicated frequency channel is both costly and inefficient. Thus, there is a need for a method and apparatus for assessing path loss without setting aside an otherwise active frequency channel or disturbing the frequency use plan.